These strange spherical boulders on the Mendocino coast in Northern California are revealed only during low tide. Resembling bowling balls they are actually called concretions and were formed as the softer surrounding sandstone was eroded by the Pacific Ocean over millions of years.
There's at least four conditions that need to be satisfied to make this photo possible. First the right time of year - the galactic core of the Milky Way is only visible during the summer season (April to September). Second is the phase of the moon - around new moon is best so that the light from the moon doesn't wash out the Milky Way. Third - the tide needs to be low otherwise the boulders are completely submerged. Finally the weather - during the summer this area is often engulfed in fog resulting in poor visibility. On Sunday night all these factors were favorable so I decided to make the 8 hour long roundtrip from San Francisco Bay Area.